This invention relates to molding compositions and articles made therefrom. More particularly, this invention relates to molding compositions for fabricating acoustic articles comprising graphite powder and a polymer, and acoustic diaphragms, arm pipes and head shells made therefrom.
For the fabrication of elements used in acoustic instruments such as diaphragms in speakers and arm pipes and head shells in record players, light weight materials are required having a high modulus of elasticity. Typical of such materials are metals such as aluminum, titanium and beryllium, and composite materials such as CFRP (carbon fiber reinforced plastics) and graphite in synthetic resins.
Since metallic materials are poor in internal loss, speaker diaphragms made therefrom have shortcomings that sound pressure is remarkably increased around resonance frequencies in the high region of a reproduction frequency range and the damping characteristics are poor. On the other hand, paper, synthetic resins and their composite materials are known as having sufficient internal loss. These materials, however, have an insufficient modulus of elasticity for speaker diaphragms made therefrom to reproduce high frequency sound and hence, to provide a wide frequency range.
Similar discussion is made on elements used in a tonearm system. It is desired to reduce the mass of a vibration system to improve the compliance of a cartridge. Further, the increased internal loss of the system is desired to prevent partial vibration. A reduction of the mass of a vibration system can be achieved by providing a light-weight arm pipe and head shell. When the wall thickness of such an element is thin for the purpose of light weight, undesired partial vibration tends to occur, which adversely affects sound quality. For this reason, light weight materials having high stiffness and hence, a sufficient specific modulus of elasticity as well as an increased internal loss are desired for the fabrication of arm pipes and head shells.
Metallic arm pipes and head shells have a high specific modulus of elasticity, but have a poor internal loss. Carbon fiber itself has a high specific modulus of elasticity and a relatively high internal loss. However, carbon fiber must be bound by a synthetic resin into a composite material in order to fabricate a shaped article. The addition of a synthetic resin reduces the specific modulus of a composite material.
The inventors previously proposed diaphragms, arm pipes and head shells made from a kneaded mixture of flaky graphite and a high molecular compound. Articles molded from such compositions, surface oxidized articles and carbonized articles are disclosed in U.S. Ser Nos. 968,912 (filed Dec. 13, 1978) U.S. Pat. No. 4,221,773, issued Sept. 9, 1980, 53,425 (filed June 29, 1979) now abandoned, 63,531 (filed Aug. 3, 1979) U.S. Pat. No. 4,261,580, issued Apr. 14, 1981, 63,532 (filed Aug. 3, 1979) U.S. Pat. No. 4,269,416, issued May 26, 1981, and 78,045 (filed Sept. 24, 1979). These materials are relatively light weight and have a high modulus of elasticity and a high internal loss. Diaphragms, arm pipes and head shells made therefrom show good properties for their purposes.